It would be incredibly easy for them to flashback in Cap 2 to Bucky on that table and show him being experimented on to explain how he'd survive the fall and any other possible augmentations to his strength, etc.

Nicely done. Haven't seen the Director's Commentary, but this serves two purposes: (1) Establish a somewhat plausible reason for Bucky being able to survive the fall, and (2) Well, he does fall under the 'super soldier' rubric... so this gives him a bit of a head start.